In order to achieve improved vehicle fuel economy, it is desirable to operate a vehicle featuring an automatic transmission, such as a continuously-variable-ratio transmission (CVT), driven through a lockup torque converter such that the torque converter operates in its fully-engaged or “locked” state as often as possible, i.e., over a wide range of vehicle speeds and driving conditions.
If the torque converter remains in the locked state during a vehicle deceleration characterized by a reduction in, or perhaps even a cessation of, fuel flow to the engine (the latter being a “fuel injectors off” condition, which necessarily achieves the greatest vehicle fuel economy), the resulting vehicle deceleration is typically quite smooth. Unfortunately, if the torque converter is still in a locked or partially-locked state when fuel flow to the engine is resumed (a “fuel injectors on” condition”) or relatively increased, the resulting engine torque as transmitted through the locked or partially-locked torque converter can disadvantageously produce an unintended or unexpected sensation of change, which is sometimes referred to as a “surge” or “bump.”
What is needed is a method and code for controlling the delivery of fuel to an engine coupled through a lock-up torque converter to an automatic transmission, such as a CVT, that reduces the likelihood of such an undesirable sensation of change, surge, or bump when the engine transitions from “fuel injectors off” to “fuel injectors on” and the torque converter is not yet in the unlocked state.